You are currently viewing our boards as a guest which gives you limited access to view most discussions and access our other features. By joining our free community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is fast, simple and absolutely free so please, join our community today!

As title states... Has anyone run a 3.91 LSD in their track car? I have found during the last 4 events I have done that my car is needing a higher gear. Currently I have a 3.15 LSD in my car and it has been a very good upgrade, but it seems I am still out of the powerband of my motor during 3rd gear corners, especially at TMP. I found the same thing at shannonville but it was not quite as bad. My only concern is running out of gear on the TMP/Shannonville straights which are 4th gear. Mosport is of no concern as 5th gets me to 215KPH and with my lightly modified motor, I won't be seeing those numbers anyways. So far, I have done mid 1:23's at TMP and I am looking to take the GT2 track record during this weekends OTA event but to do so, I need a little more. In preparation for this weekends event, I have so far removed the complete A/C system, AUX fan, fan clutch and installed a SPAL electric fan kit. Along with all of that, I will be finally installing my M50 manifold w/tune!

Btw, I am only looking for first hand experience as I have already done my research and know what numbers(speed wise) to expect! This is a track only car.

I love it - I basically always run 3-4-5, and never have to drop to 2. With my motor (built M52 - 232WHP), I don't run out of gear at Calabogie, Shannonville, and just BARELY at Mosport on a good run, but nothing serious .... watch some of my vids and you'll see my shift points.

I love it - I basically always run 3-4-5, and never have to drop to 2. With my motor (built M52 - 232WHP), I don't run out of gear at Calabogie, Shannonville, and just BARELY at Mosport on a good run, but nothing serious .... watch some of my vids and you'll see my shift points.

Is that a large case, or medium case your running?

If its the med case, have you had any issues with boiling the fluid or durability?

Thanks for the response! I wasn't worried about topping out in fifth, just 4th gear. Having to shift to 5th before turn one at TMP or after the back straight at SMP would not be good but judging by what your saying, I should still be ok.

Btw, what time have you done at SMP Long? I just did a time attack event a couple weeks back and managed a 2:03.8.

I've only ever been to shannonville twice, and it's never been a timed event. On that vid I think my best is a 2:02-2:03, just judging by the clock at the bottom lol... i didn't have many (if any) clean laps - always stuck in traffic, a couple drifts...

Last year I was sitting at around 2500lbs (plus me and the passenger), on 255/40R17 starspecs

If you watch my SMP video starting at 7:45, you'll see that I lied lol. I take that tight corner in 2nd, then do 2-3-4-5 on the back straight - you'll see there's lots of room to keep accelerating before the downshift back to 4th for the right-hander.

Again, not "declaring the law" for how to drive that track, as I don't have much experience on it.

No I've never had any issues, and I don't even run a finned cover. I had Royal Purple 75W140 in it for the past 2 years (before that was OEM fluid). Last year the input seal started leaking and I changed the fluid this year to Redline 75w90.

When I bought the car in 2005, the diff was already in, and it's now on it's 4th season of autocross/track and still holding strong!

Well, I think I have my answer based on this past weekends OTA event at TMP. If I were to switch to the 3.91, I would have to shift into fourth through the short shoot before the chicane which would not be ideal. Good thing I didn't make the move on the diff before the weekend. I was however able to remove my fan clutch, AUX fan and A/C before the weekend and I bettered my PB by a few tenths. Now sitting at a 1:23.3 In the next couple weeks I will most likely try out a 3.38 LSD and see if there is an improvement along with the M50 manifold swap.